The present invention relates to the purification of the anthelmintic compound known as moxidectin. The chemical name for moxidectin is [6R,23E,25S(E)]-5-O-Dementhyl-28-deoxy-25-(1,3-dimethyl-11-butenyl0-6,28-epoxy-23-9methoxyimino)milbemycin B. The composition of moxidectin and various uses thereof are described in U.S. Pat. No. 4,916,154, Asato, et. al, and in U.S. Pat. No. 4,900,753, Sutherland, et. al. The morphological characteristics, compounds and methods of production for moxidectin are further disclosed in U.S. Pat. No. 5,106,994, and in its issued European counterpart, EP 170,006. Another process used to purify moxidectin is disclosed in U.S. Pat. No. 4,988,824.
Moxidectin is useful as an anti-parasitic in the prevention, treatment or control of helmintic, ectoparasitic, insect, acarid and nematode infections and infestations in warm-blooded animals, as well as agricultural crops. It is especially useful to cattle and sheep farmers to control such parasites as ticks and worms. Moxidectin may be administered to livestock and other animals in a number of ways including, as a topical or “drench”, as a subcutaneous injection, or orally in pill or tablet form.
Two methods currently used to purify moxidectin are described as examples 17 and 19 of U.S. Pat. No. 4,988,824. The methods of examples 17 and 19 yield purity levels of 89% and 71%, respectively. Another process currently known and used to purify moxidectin involves the following steps: dissolving moxidectin in cyclomethylhexane, (MCH), and adding water to the moxidectin/MCH solution resulting in the precipitation of moxidectin over an extended period of time. The process results in a product with 90-92% purity, but can take days to complete. The current methods are cost-intensive, time-consuming and result in an end product with a purity level that is not high enough for many applications.
A higher purity level would further enable suitable formulations of pharmaceutical preparations for animal, as well as human uses. A method that would allow for amorphous moxidectin to be converted to crystalline moxidectin with a higher purity would also be useful to the skilled artisan.
Other methods of moxidectin currently available to the skilled artisan may achieve a higher purity level, but typically will utilize more hazardous solvents such as chloroform and dichloromethane. They also can involve more complicated processes such as normal and reverse chromatography steps (silica media).
Therefore, what is needed in the art is a new method to purify moxidectin that is cost-effective, less time consuming, and produces an end product with a higher purity level than is currently available. Also needed is moxidectin with a higher purity level than what is otherwise available in the art that is safe for use in a wide variety of pharmaceutical applications, including those for animal and even human uses.